The invention relates to implantable devices, and, in particular, to anchors that secure implantable medical devices.
Implantable medical devices, such as blood filters, stents, and grafts, are deployed within a body, for example, in a blood vessel, during both surgical and non-surgical medical procedures. An anchor secures the device in place by either piercing or pressing outwardly against the wall of the blood vessel. A physician compresses the medical device and inserts the device into the blood vessel. When the device expands, the anchor engages the wall of the blood vessel to secure the implantable medical device. In addition, other types of medical devices require anchoring within the body generally, such as valves, pacing leads, tethered devices that are removable, embolic devices, and infusion devices. A physician places such devices in, for example, blood vessels, intestines, other lumens, and other portions of the body.
For example, referring to FIG. 1, a prior art blood filter 10 resides within a lumen, for example, a blood vessel 12. Filter 10 prevents clots in the blood from flowing within blood vessel 12 to other areas of the body located downstream of filter, especially the heart, lungs, and brain. Filter 10 is generally conical and has a set of six corrugated (or zig-zagged) arms 16 that extend from an apical end 17. Arms 16 act in conjunction with each other to filter clots from the blood. Typically, filter 10 is compressed within a delivery sleeve (not shown) at the end of a catheter. A physician inserts the compressed filter 10 into a lumen such as blood vessel 12. Once filter 10 is inside blood vessel 12, the physician removes the delivery sleeve, and filter 10 expands. Arms 16 exert a radial force transverse to a central axis 24 of the filter 10 against a wall 22 of vessel 12.
Each arm 16 has a corresponding end 18 that forms one of six hooks 14a-14f. When filter 10 expands into the position shown in FIG. 1, hooks 14a-14f engage with wall 22, preventing filter 10 from migrating within blood vessel 12, for example, the vena cava. Each hook 14a-14f terminates at a corresponding point 20. The radial force of arms 16 causes points 20 to pierce wall 22. Hooks 14a, 14c, 14d, and 14f each have a corresponding point 20 oriented in the direction of blood flow. Thus, hooks 14a, 14c, 14d, and 14f counteract the force of the blood rushing through filter 10 and prevent the migration of filter 10 within blood vessel 12. In addition, hooks 14b and 14e each have corresponding points 20 that are oriented in the direction opposite the blood-flow. Thus, hooks 14b and 14e prevent migration of filter in the direction opposite the blood flow, which may be caused, for example, by movement of the body.
Referring to FIGS. 2 and 3, another type of prior art blood clot filter 32 includes a wire mesh 34. Wire mesh 34 has a cylindrical portion 36 and a conical portion 38. Conical portion 38 extends from an apical end 40. An opposite end 44 of filter 32 includes an opening 46 that allows blood and clots to flow into filter 32. Filter 32 is described in greater detail in U.S. patent application Ser. No. 09/008,258, the entire disclosure of which is incorporated herein by reference.
Filter 32 also includes anchors 30. Anchors 30 include two separate pieces: a shank 26, which defines a hollow 28, and a hook 29, which is a metallic strip centered within hollow 28. Anchors 30 attach to wire strands 42 at junctures 48 where wire strands 42 intersect. Hook 29, and two wire strands 42, extend through hollow 28. Shank 26, hook 29, and wire strands 42 are welded together.
An implantable medical device, such as filter 10 or filter 32, typically must be compressible to a diameter smaller than the diameter of the body lumen in which it is to be implanted. The compressed diameter of the device thus limits its use. Anchoring devices, such as hooks 14a-14f or anchors 30, have profiles that limit the contraction of a blood filter or other medical device.